Super-Simple Shortwave Receiver Circuit

Integrated circuit Ul (an NE602 double-balanced mixer) is a combination oscillator and frequency mixer. Signals from the antenna input (at Jl) are fed through dc-blocking capacitor C1 to the RF-gain control, Rl, and fed to the input of Ul at pins 1 and 2. The local-oscillator frequency, which varies with the settings of R2 and L2, is mixed internally within Ul, resulting in an output. The mixer output at pin 4 of Ul is applied to a tunable 260-kHz band-pass intermediate-frequency (IF) transformer, L3, tlirough dc-blocking capacitor C7.

Therefore, signals that are roughly 260 kHz above and below the local-oscillator frequency are passed while others are effectively blocked. The IF frequencies are now amplified by Q2 and Q3. The AM audio signal is detected by D2 and its associated components, which bypass the RF signals, and leave only the audio signals. The signals are preamplified by Ul -a (half of an LM358 dual op amp). The audio is then boosted to speaker level by the LM386 low-voltage audio power amplifier, U3.